JPH0771726B2 - Continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a continuous casting method, and is particularly intended to effectively avoid breakout and the like.

(Prior Art) Regarding the method of preventing breakout of a slab, which may occur when continuous casting is applied, the temperature behavior of the continuous casting mold has been used as an index so far, and specifically, (1) A method for comparing the temperature measurement data above the continuous casting mold and the temperature measurement data below the continuous casting mold in the drawing direction of the continuous casting slab (Patent Document 1)
57-115961) or (2) a method for measuring the temperature difference between the copper plate surfaces of a copper plate for forming a continuous casting mold (Japanese Patent Publication No.
56-7783), or (3) a method of predicting that a breakout will occur when the temperature detected by the thermocouple provided on the wall surface of the mold once rises and then falls below the detected average temperature (JP-A-57-152356). (See the official gazette) and the like are known.

However, the mold temperature becomes higher when the casting speed becomes faster and becomes lower when the casting speed becomes slower. Therefore, in the method of judging only the vertical movement (fluctuation) of the mold temperature as described above,
There is a problem that an accurate determination cannot be made when the powder flowing into the space between the mold and the slab is uneven or when an air gap is generated.

As a breakout prediction method including these measures, for example, (4) Japanese Patent Laid-Open No. 60-44163 discloses that the values of at least two temperature detecting ends provided on the side wall of a continuous casting mold are temporally reduced. Subsequently, there is a method of determining an abnormality when the temperature is deviated to a temperature higher than the steady level, and (5) Japanese Patent Laid-Open No. 61-289954 discloses prediction based on a plurality of set values serving as indexes of the continuous casting mold. The method is further described in (6) Japanese Patent Laid-Open No. 61-226154, in which the factor due to the change in the casting speed is determined from the measured temperature based on the relationship between the temperature at each temperature measurement point and the casting speed which is obtained in advance. After the removal, the ratio of the temperature of a predetermined measurement point to all the measurement points is obtained as a relative temperature, and when the relative temperature deviates from a preset upper or lower limit value, a method of predicting a breakout is disclosed.

(Problems to be solved by the invention) By the way, (4) in the above technique cannot predict breakout when the casting speed is changed or when the molten metal level changes, and (5) is set. Value (parameter)
There is a concern that false alarms will increase when casting conditions change.
Further, with respect to (6), when the temperature measurement position or the casting condition changes, the temperature instruction value also changes, so that it is necessary to measure the parameter each time, and there is a problem that versatility and applicability are lacking.

It is an object of the present invention to provide a continuous casting method that can realize accurate prediction without being affected by changes in casting conditions such as casting speed and fluctuations in molten metal surface.

(Means for solving the problem) The temperature measurement value of the mold during continuous casting shows similar behavior at all temperature measurement points at almost the same time due to increase / decrease in casting speed, fluctuations in the molten metal level, and components and changes in the mold powder. On the other hand, the change largely depends on the temperature measurement depth (distance from the surface of the mold copper plate to the tip of the temperature measuring element), the type of cast steel, the type of mold powder, the casting temperature, the casting speed before and after the increase and decrease, and the like.

Therefore, it is important to distinguish the temperature measurement value and the behavior of the temperature measurement value from those at the time of breakout due to the influence of these factors.

Therefore, in the present invention, the difference between the temperature change rate of each temperature measurement point of the continuous casting mold and the average temperature change rate of all temperature measurement points is obtained, and this difference is used as an index to advantageously achieve the intended purpose. It was done.

That is, according to the present invention, the temperature of the inner wall of the mold copper plate formed by the continuous casting mold is determined by a group of three or more temperature-measuring elements arranged in a row at a predetermined interval in a direction below the meniscus-equivalent portion and in a direction intersecting the slab drawing direction. The difference between the temperature change rate at each temperature measurement point and the average temperature change rate at all temperature measurement points is calculated from the measured values, and this value depends on the preset casting speed and melt level fluctuations. Do not exceed the temperature change speed set value,
In addition, if the propagation pattern due to the temporal change in the temperature change rate at each temperature measurement point matches the previously known propagation pattern at breakout, change the operating conditions to avoid the risk of breakout. Is a continuous casting method.

(Operation) According to the present invention, as shown in FIG. 1, a mold copper plate forming a continuous casting mold is provided with three or more temperature-measuring elements arranged at a predetermined interval in a direction intersecting the drawing direction of the slab and arranged in a row. Set up. Then, the temperature change rate at each temperature measurement point is obtained during continuous casting. The temperature change speed at the temperature measurement position i
_i is Further, the average temperature change rate _av of all the temperature measurement points i = 1 to n is N: Calculated based on all measured temperature points.

Then, the relative temperature change rate ▲ ^r _i ▼ is calculated from the above equations (1) and (2) by the following: ▲ ^r _i ▼ = _i - _av ... (3).

If a similar behavior of the temperature measurement value of mutual at each temperature measuring point is caused by other factors other than breakout _{i
Since av} and ▲ ^r _i ▼ = 0 ° C / s, it becomes possible to easily remove the influence of changes in casting conditions and the like.

During the abnormal period when these index values rise, the propagation pattern due to the temporal change of the temperature change rate at each temperature measurement point,
Explaining what kind of situation there is when a breakout occurs, for example, point i and (i +
It is assumed that the solidified shell is seized and fractured between points 1) or at the meniscus portion of point A near i.

Due to the progress of casting, at points i and (i + 1), ▲ ^r _i
▼ and ▲ ^r _{i + 1} ▼ are almost simultaneously, or continue to ▲ ^r _i ▼ ▲
^r _{i + 1} ▼ increases. As casting continues, (i +
2) Point and (i-1) point are ▲ ^r _{i + 2} ▼ and ▲ ^r _{i + 1 respectively}
▼ almost simultaneously or ▲ ^r _i-1 ▼ at the (i-1) point, and then ▲ ^r _{i + 2} ▼ at the (i + 2) point rises. In this way, if seizure occurs between the temperature measurement points i and (i + 1), ▲ ^r _i ▼ →
The temperature change speed increases alternately left and right (or right and left) in the order of ▲ ^r _{i + 1} ▼ → ▲ ^r _i-1 ▼ → ▲ ^r _{i + 2} ▼. If the thermocouple at the temperature measuring point is broken, for example, (i
If the thermocouple is broken at point -1), i → (i
Since the temperature rise is detected in the order of +1) → (i + 2), the temperature changes regularly and continuously in the right direction (one direction).

The above phenomenon is a characteristic immediately before the seizure (restraint) breakout occurs, and is based on the result of analysis of data of several tens of rows of temperature behavior in continuous casting.

Therefore, in the above example, an abnormality in the value obtained at each temperature measurement point adjacent to the point i is detected with reference to ▲ ^r _i ▼ at the point i, and the pattern of transmission of the abnormality (propagation pattern)
Is compared with the transmission method (propagation pattern) when the breakout occurs, and it is determined whether or not they are the same, so that highly accurate prediction is possible. In particular, the breakout in the conventional continuous casting was predicted by comparing the temperature measurement point or its temporal / spatial change rate with a specific value depending on the casting conditions. Anomalies are detected by comparing the measured values or their temporal and spatial change rates with specific values that do not depend on the casting conditions, and the time-dependent propagation pattern of the anomalies is known beforehand. Since the judgment is made by comparing with the propagation pattern peculiar to the above, the prediction accuracy can be significantly improved and the versatility is high.

It should be noted that, at the temperature measuring points adjacent to each other, the maximum time at which the time interval at which the abnormality of the measured value occurs occurs,
That is, the propagation time (T) is determined by the following equation (5) according to the temperature measuring point interval (w), the casting speed (V _c ), the solidification shell break line angle (β), and the moving speed (α · V _c ). You can ask more.

However, alpha: constant (0.5 to 1.0) also determines that the solidified shell in the mold is broken in accordance with the present invention, 'in case of decelerated to its velocity V _c' the casting speed from V _c V _c is Judge whether it is appropriate,
That is, the judgment of whether the breakout portion breaks out due to bulging just below the mold of the solidification shell when it comes out from the lower end of the mold is determined from the tip of the breaking line of the solidification shell when the breakout is predicted. To the distance L _P and the reduced casting speed V _c ′ after prediction
Then, the time t _d until deceleration may be determined so as to satisfy the following expression (6).

Where k _s : solidification rate constant of molten steel in the mold (mm−min
^-0.5 ) V _c : Casting speed (m / min) L: Mold length (mm) d _B.0 : Minimum solidified shell thickness immediately below the mold that does not break out due to _bulging (empirically determined value)
(Mm) lm: Distance from top of mold to temperature measuring point (m) n: Number of temperature measuring points used for breakout prediction judgment In the present invention, the number of temperature measuring points n should be 3 or more. However, the reason for this is that increasing the number of measured temperatures can reduce false alarms and enable accurate prediction, and it is preferable to use the maximum value that satisfies the above equation (6).

From the above explanation, the value that should be set in predicting breakout in continuous casting is the upper limit value of the temperature change rate ▲
^r _cr ▼ and ▲ ^r _i ▼ ≧ ▲ ^r _cr to prevent noise detection
The duration t is t _cr , and β, α, and n are six. Here, t _cr is a short period of time due to temperature fluctuations or temperature measuring instability during normal casting, ▲ ^r _i ▼ set value ▲ ^r _cr ▼
It is a parameter provided to eliminate false alarms when the value exceeds, and gives the lower limit of the time when ▲ ^r _i ▼ ≧ ▲ ^r _cr ▼ is satisfied. In addition, β and α can be obtained from the coagulation shell at the time of breakout or temperature measurement data, β = 20 to 45 °,
α = 0.5 to 1.0, which is a parameter that is less affected by casting conditions. Further, n is the above (6) if the temperature measurement position is determined,
It has the property given by the equation (7). Therefore, the setting parameters are the upper limit value of temperature change rate ▲ ^r _cr ▼ and _i
≧ _cr the time t _cr satisfying the will substantially be may be determined two parameters empirically. This 2
The individual parameters are parameters that do not substantially depend on the above operating conditions, and are not significantly affected by differences in casting conditions such as the type of continuous casting machine, target steel type, casting speed, or slab size, and are obtained in the past. It is set based on the temperature behavior of the mold copper plate during the specified breakout.

(Example) According to the system as shown in FIG. 2, continuous casting was performed under the casting conditions and temperature measurement conditions shown in Table 1 while predicting breakout.

Table 2 shows the results of investigating the breakout prediction accuracy when the present invention is applied, as a comparative example (Japanese Patent Laid-Open No. 61-
(226154 gazette) is shown together with the results of investigation of the prediction accuracy of breakout.

FIG. 3 is a graph showing the change over time in the temperature change rate at the time of prediction in correspondence with the mold copper plate temperature, the casting speed (V _c ), and the melt level fluctuation amount (M _L ).

From the 3rd appendix, the rate of temperature change ▲ ^r _i ▼ even if V _c and M _L change
It can be seen that is almost unchanged. This operation is shown when the casting speed is reduced at that position because the breakout prediction alarm sounds at the arrowed portion in the figure. After that, when the surface of the slab that was located in the mold where the alarm sounded was investigated, it was shown that the restraint breakout had progressed on the surface.
The marking of the mold was observed, and it was confirmed that the prediction of breakout according to the present invention was extremely effective.

(Effect of the Invention) According to the present invention, the change of the casting speed in continuous casting,
Accurate breakout prediction is possible without being affected by conditions such as changes in the molten metal surface, changes in mold powder components, temperature measurement depth, differences in target steel grades, casting size, etc. Therefore, the frequency of deceleration is extremely reduced, so there is no decrease in productivity. Also,
Since the number of setting parameters required for predictive judgment is small, it can be applied to continuous casters of different types and is highly versatile.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a main part of a continuous casting mold, FIG. 2 is a schematic view of a prediction system suitable for carrying out the present invention, and FIG. 3 is a temperature change. Speed, mold copper plate temperature, casting speed,
It is a graph showing the relationship of the level fluctuation level.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Keisuke Yamanaka 1 Kawasaki-cho, Chiba-shi, Chiba Inside Kawasaki Steel Co., Ltd. (72) Inventor Hiroaki Iguchi 1-Kawasaki-cho, Chiba Chiba Kawasaki Inside the Steel Works (72) Inventor Bessho Nagayasu No. 1 Kawasaki Town, Chiba City, Chiba Prefecture Inside the Technical Research Division, Kawasaki Steel Co., Ltd. (56) References JP 63-115660 (JP, A) JP 61-46362 (JP, A) JP-A-57-115962 (JP, A)

Claims (1)

[Claims] 1. The temperature of the inner wall of a copper plate for forming a continuous casting mold is determined by a group of three or more temperature-measuring elements arranged in a row at a predetermined interval in a direction below the portion corresponding to the meniscus and intersecting with the slab drawing direction. The difference between the temperature change rate at each temperature measurement point and the average temperature change rate at all temperature measurement points is calculated from the obtained measurement values, and this value does not depend on the preset casting speed and melt level fluctuations. Risk of breakout if the temperature change rate exceeds the set value and the propagation pattern due to the temporal change of the temperature change rate at each temperature measurement point matches the previously known propagation pattern at breakout. A continuous casting method, characterized in that the operating conditions are changed to avoid the above.